From the Tomcat Alley Webpage F-14A Plus History
In the Tomcat's entire history it's biggest and most recurrent problem had been the power plant. Ever since the start of the VFX program, the TF-30 was recognised as an imperfect engine for the requirements. The original intention was that it would power only the first batches of F-14's. After two years production would switch to the F-14B, featuring the Pratt & Whitney F-401-P400 engine and all F-14A's would be upgraded to F-14B standard. Like most good plans, this fell through for a number of reasons and the Navy was left with theTF-30 to power the F-14. Although more reliable and safer variants of the TF-30 have come along since it is still the F-14's biggest weakness and the Navy was always interested in a better engine. Then in the early 1980's along came the General Electric F-110 turbofan and it is here that the F-14A Plus story begins.
Note: The F-14A Plus is now known as the F-14B, due, I believe, to problems with the Navy's computers in accepting the A+ designation. As mentioned above the F-14B designation had already been used, albeit for a single prototype.
http://www.topedge.com/alley/text/f14b/f14b.htm
Fighter Fling 2004: https://www.youtube.com/watch?v=92ZbKXwQ1u8
RF-4Cs of the Nevada Air National Guard: https://www.youtube.com/watch?v=YmXvQqEcJZ8&t=62s